Auto merge of rust-lang#121589 - bvanjoi:fix-98291, r=petrochenkov

delay expand macro bang when there has indeterminate path

Related rust-lang#98291

I will attempt to clarify the root problem through several examples:

Firstly,

```rs
// rustc code.rs --edition=2018

macro_rules! wrap {
    () => {
        macro_rules! _a {
            () => {
                "Hello world"
            };
        }
    };
}

wrap!();

use _a as a;

fn main() {
    format_args!(_a!());
}
```

The above case will compile successfully because `_a` is defined after the `wrap` expaned, ensuring `_a` can be resolved without any issues.

And,

```rs
// rustc code.rs --edition=2018

macro_rules! wrap {
    () => {
        macro_rules! _a {
            () => {
                "Hello world"
            };
        }
    };
}

wrap!();

use _a as a;

fn main() {
    format_args!("{}", a!());
}
```

The above example will also compile successfully because the `parse_args` in `expand_format_args_impl` will return a value `MacroInput { fmtstr: Expr::Lit::Str, args: [Expr::MacroCall]}`. Since the graph for `args` will be build lately, `a` will eventually be resolved.

However, in the case of:

```rs
// rustc code.rs --edition=2018

macro_rules! wrap {
    () => {
        macro_rules! _a {
            () => {
                "Hello world"
            };
        }
    };
}

wrap!();

use _a as a;

fn main() {
    format_args!(a!());
}
```

The result of `parse_args` is `MacroInput {fmtstr: Expr::Lit::Macro, args: [] }`, we attempt to expand `fmtstr` **eagerly** within `expr_to_spanned_string`. Although we have recorded `(root, _a)` into resolutions, `use _a as a` is an indeterminate import, which will not try to resolve under the conditions of `expander.monotonic = false`.

Therefore, I've altered the strategy for resolving indeterminate imports, ensuring it will also resolve during eager expansion. This could be a significant change to the resolution infra. However, I think it's acceptable if the goal of avoiding resolution under eager expansion is to save time.

r? `@petrochenkov`

compiler/rustc_builtin_macros/src/asm.rs

@@ -5,7 +5,7 @@ use rustc_ast::token::{self, Delimiter};
 use rustc_ast::tokenstream::TokenStream;
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_errors::PResult;
-use rustc_expand::base::{self, *};
+use rustc_expand::base::*;
 use rustc_index::bit_set::GrowableBitSet;
 use rustc_parse::parser::Parser;
 use rustc_parse_format as parse;
@@ -443,7 +443,7 @@ fn parse_reg<'a>(
 fn expand_preparsed_asm(
     ecx: &mut ExtCtxt<'_>,
     args: AsmArgs,
-) -> Result<ast::InlineAsm, ErrorGuaranteed> {
+) -> ExpandResult<Result<ast::InlineAsm, ErrorGuaranteed>, ()> {
     let mut template = vec![];
     // Register operands are implicitly used since they are not allowed to be
     // referenced in the template string.
@@ -465,16 +465,20 @@ fn expand_preparsed_asm(
 
         let msg = "asm template must be a string literal";
         let template_sp = template_expr.span;
-        let (template_str, template_style, template_span) =
-            match expr_to_spanned_string(ecx, template_expr, msg) {
+        let (template_str, template_style, template_span) = {
+            let ExpandResult::Ready(mac) = expr_to_spanned_string(ecx, template_expr, msg) else {
+                return ExpandResult::Retry(());
+            };
+            match mac {
                 Ok(template_part) => template_part,
                 Err(err) => {
-                    return Err(match err {
+                    return ExpandResult::Ready(Err(match err {
                         Ok((err, _)) => err.emit(),
                         Err(guar) => guar,
-                    });
+                    }));
                 }
-            };
+            }
+        };
 
         let str_style = match template_style {
             ast::StrStyle::Cooked => None,
@@ -562,7 +566,7 @@ fn expand_preparsed_asm(
                 e.span_label(err_sp, label);
             }
             let guar = e.emit();
-            return Err(guar);
+            return ExpandResult::Ready(Err(guar));
         }
 
         curarg = parser.curarg;
@@ -729,24 +733,27 @@ fn expand_preparsed_asm(
         }
     }
 
-    Ok(ast::InlineAsm {
+    ExpandResult::Ready(Ok(ast::InlineAsm {
         template,
         template_strs: template_strs.into_boxed_slice(),
         operands: args.operands,
         clobber_abis: args.clobber_abis,
         options: args.options,
         line_spans,
-    })
+    }))
 }
 
 pub(super) fn expand_asm<'cx>(
     ecx: &'cx mut ExtCtxt<'_>,
     sp: Span,
     tts: TokenStream,
-) -> Box<dyn base::MacResult + 'cx> {
-    match parse_args(ecx, sp, tts, false) {
+) -> MacroExpanderResult<'cx> {
+    ExpandResult::Ready(match parse_args(ecx, sp, tts, false) {
         Ok(args) => {
-            let expr = match expand_preparsed_asm(ecx, args) {
+            let ExpandResult::Ready(mac) = expand_preparsed_asm(ecx, args) else {
+                return ExpandResult::Retry(());
+            };
+            let expr = match mac {
                 Ok(inline_asm) => P(ast::Expr {
                     id: ast::DUMMY_NODE_ID,
                     kind: ast::ExprKind::InlineAsm(P(inline_asm)),
@@ -762,34 +769,39 @@ pub(super) fn expand_asm<'cx>(
             let guar = err.emit();
             DummyResult::any(sp, guar)
         }
-    }
+    })
 }
 
 pub(super) fn expand_global_asm<'cx>(
     ecx: &'cx mut ExtCtxt<'_>,
     sp: Span,
     tts: TokenStream,
-) -> Box<dyn base::MacResult + 'cx> {
-    match parse_args(ecx, sp, tts, true) {
-        Ok(args) => match expand_preparsed_asm(ecx, args) {
-            Ok(inline_asm) => MacEager::items(smallvec![P(ast::Item {
-                ident: Ident::empty(),
-                attrs: ast::AttrVec::new(),
-                id: ast::DUMMY_NODE_ID,
-                kind: ast::ItemKind::GlobalAsm(Box::new(inline_asm)),
-                vis: ast::Visibility {
-                    span: sp.shrink_to_lo(),
-                    kind: ast::VisibilityKind::Inherited,
+) -> MacroExpanderResult<'cx> {
+    ExpandResult::Ready(match parse_args(ecx, sp, tts, true) {
+        Ok(args) => {
+            let ExpandResult::Ready(mac) = expand_preparsed_asm(ecx, args) else {
+                return ExpandResult::Retry(());
+            };
+            match mac {
+                Ok(inline_asm) => MacEager::items(smallvec![P(ast::Item {
+                    ident: Ident::empty(),
+                    attrs: ast::AttrVec::new(),
+                    id: ast::DUMMY_NODE_ID,
+                    kind: ast::ItemKind::GlobalAsm(Box::new(inline_asm)),
+                    vis: ast::Visibility {
+                        span: sp.shrink_to_lo(),
+                        kind: ast::VisibilityKind::Inherited,
+                        tokens: None,
+                    },
+                    span: sp,
                     tokens: None,
-                },
-                span: sp,
-                tokens: None,
-            })]),
-            Err(guar) => DummyResult::any(sp, guar),
-        },
+                })]),
+                Err(guar) => DummyResult::any(sp, guar),
+            }
+        }
         Err(err) => {
             let guar = err.emit();
             DummyResult::any(sp, guar)
         }
-    }
+    })
 }

compiler/rustc_builtin_macros/src/assert.rs

@@ -9,7 +9,7 @@ use rustc_ast::tokenstream::{DelimSpan, TokenStream};
 use rustc_ast::{DelimArgs, Expr, ExprKind, MacCall, Path, PathSegment, UnOp};
 use rustc_ast_pretty::pprust;
 use rustc_errors::PResult;
-use rustc_expand::base::{DummyResult, ExtCtxt, MacEager, MacResult};
+use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacEager, MacroExpanderResult};
 use rustc_parse::parser::Parser;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
@@ -19,12 +19,12 @@ pub fn expand_assert<'cx>(
     cx: &'cx mut ExtCtxt<'_>,
     span: Span,
     tts: TokenStream,
-) -> Box<dyn MacResult + 'cx> {
+) -> MacroExpanderResult<'cx> {
     let Assert { cond_expr, custom_message } = match parse_assert(cx, span, tts) {
         Ok(assert) => assert,
         Err(err) => {
             let guar = err.emit();
-            return DummyResult::any(span, guar);
+            return ExpandResult::Ready(DummyResult::any(span, guar));
         }
     };
 
@@ -92,7 +92,7 @@ pub fn expand_assert<'cx>(
         expr_if_not(cx, call_site_span, cond_expr, then, None)
     };
 
-    MacEager::expr(expr)
+    ExpandResult::Ready(MacEager::expr(expr))
 }
 
 struct Assert {

compiler/rustc_builtin_macros/src/cfg.rs

@@ -8,17 +8,17 @@ use rustc_ast::token;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_attr as attr;
 use rustc_errors::PResult;
-use rustc_expand::base::{DummyResult, ExtCtxt, MacEager, MacResult};
+use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacEager, MacroExpanderResult};
 use rustc_span::Span;
 
 pub fn expand_cfg(
     cx: &mut ExtCtxt<'_>,
     sp: Span,
     tts: TokenStream,
-) -> Box<dyn MacResult + 'static> {
+) -> MacroExpanderResult<'static> {
     let sp = cx.with_def_site_ctxt(sp);
 
-    match parse_cfg(cx, sp, tts) {
+    ExpandResult::Ready(match parse_cfg(cx, sp, tts) {
         Ok(cfg) => {
             let matches_cfg = attr::cfg_matches(
                 &cfg,
@@ -32,7 +32,7 @@ pub fn expand_cfg(
             let guar = err.emit();
             DummyResult::any(sp, guar)
         }
-    }
+    })
 }
 
 fn parse_cfg<'a>(cx: &mut ExtCtxt<'a>, span: Span, tts: TokenStream) -> PResult<'a, ast::MetaItem> {

compiler/rustc_builtin_macros/src/compile_error.rs

@@ -1,22 +1,26 @@
 // The compiler code necessary to support the compile_error! extension.
 
 use rustc_ast::tokenstream::TokenStream;
-use rustc_expand::base::{get_single_str_from_tts, DummyResult, ExtCtxt, MacResult};
+use rustc_expand::base::get_single_str_from_tts;
+use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacroExpanderResult};
 use rustc_span::Span;
 
 pub fn expand_compile_error<'cx>(
     cx: &'cx mut ExtCtxt<'_>,
     sp: Span,
     tts: TokenStream,
-) -> Box<dyn MacResult + 'cx> {
-    let var = match get_single_str_from_tts(cx, sp, tts, "compile_error!") {
+) -> MacroExpanderResult<'cx> {
+    let ExpandResult::Ready(mac) = get_single_str_from_tts(cx, sp, tts, "compile_error!") else {
+        return ExpandResult::Retry(());
+    };
+    let var = match mac {
         Ok(var) => var,
-        Err(guar) => return DummyResult::any(sp, guar),
+        Err(guar) => return ExpandResult::Ready(DummyResult::any(sp, guar)),
     };
 
     #[expect(rustc::diagnostic_outside_of_impl, reason = "diagnostic message is specified by user")]
     #[expect(rustc::untranslatable_diagnostic, reason = "diagnostic message is specified by user")]
     let guar = cx.dcx().span_err(sp, var.to_string());
 
-    DummyResult::any(sp, guar)
+    ExpandResult::Ready(DummyResult::any(sp, guar))
 }

compiler/rustc_builtin_macros/src/concat.rs

@@ -1,6 +1,7 @@
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{ExprKind, LitKind, UnOp};
-use rustc_expand::base::{get_exprs_from_tts, DummyResult, ExtCtxt, MacEager, MacResult};
+use rustc_expand::base::get_exprs_from_tts;
+use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacEager, MacroExpanderResult};
 use rustc_session::errors::report_lit_error;
 use rustc_span::symbol::Symbol;
 
@@ -10,10 +11,13 @@ pub fn expand_concat(
     cx: &mut ExtCtxt<'_>,
     sp: rustc_span::Span,
     tts: TokenStream,
-) -> Box<dyn MacResult + 'static> {
-    let es = match get_exprs_from_tts(cx, tts) {
+) -> MacroExpanderResult<'static> {
+    let ExpandResult::Ready(mac) = get_exprs_from_tts(cx, tts) else {
+        return ExpandResult::Retry(());
+    };
+    let es = match mac {
         Ok(es) => es,
-        Err(guar) => return DummyResult::any(sp, guar),
+        Err(guar) => return ExpandResult::Ready(DummyResult::any(sp, guar)),
     };
     let mut accumulator = String::new();
     let mut missing_literal = vec![];
@@ -70,12 +74,13 @@ pub fn expand_concat(
         }
     }
 
-    if !missing_literal.is_empty() {
+    ExpandResult::Ready(if !missing_literal.is_empty() {
         let guar = cx.dcx().emit_err(errors::ConcatMissingLiteral { spans: missing_literal });
-        return DummyResult::any(sp, guar);
+        DummyResult::any(sp, guar)
     } else if let Some(guar) = guar {
-        return DummyResult::any(sp, guar);
-    }
-    let sp = cx.with_def_site_ctxt(sp);
-    MacEager::expr(cx.expr_str(sp, Symbol::intern(&accumulator)))
+        DummyResult::any(sp, guar)
+    } else {
+        let sp = cx.with_def_site_ctxt(sp);
+        MacEager::expr(cx.expr_str(sp, Symbol::intern(&accumulator)))
+    })
 }

compiler/rustc_builtin_macros/src/concat_bytes.rs

@@ -1,5 +1,6 @@
 use rustc_ast::{ptr::P, token, tokenstream::TokenStream, ExprKind, LitIntType, LitKind, UintTy};
-use rustc_expand::base::{get_exprs_from_tts, DummyResult, ExtCtxt, MacEager, MacResult};
+use rustc_expand::base::get_exprs_from_tts;
+use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacEager, MacroExpanderResult};
 use rustc_session::errors::report_lit_error;
 use rustc_span::{ErrorGuaranteed, Span};
 
@@ -111,10 +112,13 @@ pub fn expand_concat_bytes(
     cx: &mut ExtCtxt<'_>,
     sp: Span,
     tts: TokenStream,
-) -> Box<dyn MacResult + 'static> {
-    let es = match get_exprs_from_tts(cx, tts) {
+) -> MacroExpanderResult<'static> {
+    let ExpandResult::Ready(mac) = get_exprs_from_tts(cx, tts) else {
+        return ExpandResult::Retry(());
+    };
+    let es = match mac {
         Ok(es) => es,
-        Err(guar) => return DummyResult::any(sp, guar),
+        Err(guar) => return ExpandResult::Ready(DummyResult::any(sp, guar)),
     };
     let mut accumulator = Vec::new();
     let mut missing_literals = vec![];
@@ -170,12 +174,13 @@ pub fn expand_concat_bytes(
             }
         }
     }
-    if !missing_literals.is_empty() {
+    ExpandResult::Ready(if !missing_literals.is_empty() {
         let guar = cx.dcx().emit_err(errors::ConcatBytesMissingLiteral { spans: missing_literals });
-        return MacEager::expr(DummyResult::raw_expr(sp, Some(guar)));
+        MacEager::expr(DummyResult::raw_expr(sp, Some(guar)))
     } else if let Some(guar) = guar {
-        return MacEager::expr(DummyResult::raw_expr(sp, Some(guar)));
-    }
-    let sp = cx.with_def_site_ctxt(sp);
-    MacEager::expr(cx.expr_byte_str(sp, accumulator))
+        MacEager::expr(DummyResult::raw_expr(sp, Some(guar)))
+    } else {
+        let sp = cx.with_def_site_ctxt(sp);
+        MacEager::expr(cx.expr_byte_str(sp, accumulator))
+    })
 }

compiler/rustc_builtin_macros/src/concat_idents.rs

@@ -2,7 +2,7 @@ use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Token};
 use rustc_ast::tokenstream::{TokenStream, TokenTree};
 use rustc_ast::{AttrVec, Expr, ExprKind, Path, Ty, TyKind, DUMMY_NODE_ID};
-use rustc_expand::base::{DummyResult, ExtCtxt, MacResult};
+use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacResult, MacroExpanderResult};
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::Span;
 
@@ -12,10 +12,10 @@ pub fn expand_concat_idents<'cx>(
     cx: &'cx mut ExtCtxt<'_>,
     sp: Span,
     tts: TokenStream,
-) -> Box<dyn MacResult + 'cx> {
+) -> MacroExpanderResult<'cx> {
     if tts.is_empty() {
         let guar = cx.dcx().emit_err(errors::ConcatIdentsMissingArgs { span: sp });
-        return DummyResult::any(sp, guar);
+        return ExpandResult::Ready(DummyResult::any(sp, guar));
     }
 
     let mut res_str = String::new();
@@ -25,7 +25,7 @@ pub fn expand_concat_idents<'cx>(
                 TokenTree::Token(Token { kind: token::Comma, .. }, _) => {}
                 _ => {
                     let guar = cx.dcx().emit_err(errors::ConcatIdentsMissingComma { span: sp });
-                    return DummyResult::any(sp, guar);
+                    return ExpandResult::Ready(DummyResult::any(sp, guar));
                 }
             }
         } else {
@@ -37,7 +37,7 @@ pub fn expand_concat_idents<'cx>(
             }
 
             let guar = cx.dcx().emit_err(errors::ConcatIdentsIdentArgs { span: sp });
-            return DummyResult::any(sp, guar);
+            return ExpandResult::Ready(DummyResult::any(sp, guar));
         }
     }
 
@@ -68,5 +68,5 @@ pub fn expand_concat_idents<'cx>(
         }
     }
 
-    Box::new(ConcatIdentsResult { ident })
+    ExpandResult::Ready(Box::new(ConcatIdentsResult { ident }))
 }